Some printing apparatus drops ink onto a sheet once or a plurality of times on the basis of printing data and the like and forms an image. If the printing apparatus drops the ink a plurality of times, the viscosity of the ink changes because of thixotropy and the like of the ink. The discharge speeds, the volumes, and the like of respective drops change. Therefore, the printing quality of the printing apparatus is unstable.
An example of the related art is described in JP-A-2005-153378.